Microbially induced magnesium carbonation reactions as a strategy for carbon sequestration in ultramafic mine tailings

The atmospheric carbon dioxide (CO2) concentration has increased due to anthropogenic fossil fuel combustion, causing higher global temperatures and other negative environmental effects. CO2 sequestration through carbonate mineralisation provides a stable, long term carbon sink. A natural hydromagnesite playa (Atlin, British Columbia, Canada) demonstrates the ability of phototrophic microorganisms to accelerate magnesium carbonate mineralisation. The site’s biogeochemistry was modeled in a 10 m flow-through bioreactor carbonation experiment, allowing for hydromagnesite precipitation conditions to be refined. Ultramafic mine tailings are a target substrate for carbonation reactions due to their high magnesium content. A synthetic mine leach water, designed from the results of a chrysotile leaching experiment, was added to the bioreactor in a second carbonation experiment. This demonstrated the microorganisms’ ability to precipitate hydromagnesite and magnesite using atmospheric CO2. The achieved carbon storage rate of 65 t C/ha/year has the potential to offset net carbon emissions of mining operations